Fuel flowing back after couple of days (super bee 1970)

[madhouse]

Hi I have a Super Bee 1970 - 383 - with new tanked placed by previous owner. It had an electric fuel pump. I got the pump removed (was very noisy) and replaced by a mechanical one on the engine (and new inline filter). Initially OK. But when I leave the car for a few days the fuel has flowed back to the tank. It then takes a couple of cranks (5 or 6 generally) to get enough fuel and pressure back to start. Once started it runs fine.

where do I start looking or fixing (to avoid putting a new electric pump in)...? There are 2 outlets on the short side of the tank. One is sealed off - the other runs the single line to the front.

thanks
chr.

 

[69Bee]

Both are vents. One vents right at the tank, and the other runs to the evaporative canister if you have one. They both should be open to air, so vacuum will not pull fuel back to the tank.

 

[Dennis H]

Sounds like a characteristic. Mine has an electric pump and requires 3 to the floor after setting for a while. You mean 6 attempts or 6 spins on one attempt? Turning the ignition on for a few seconds to let the electric pump run prior to spinning the starter does not seem to make a difference.

 

[lewtot184]

fuel isn't "flowing back"; it's evaporating.

 

[krowbar]

Mine does that too. I have an electric pump in back and regulator at the fender then goes to glass filter and finally to Holley 850DP. I don't have any check valves in my bowls. I just turn on the pump and let the bowls fill. Give the throttle one pump and crank it and fires right up. What kind of mechanical pump did you put on?

 

[69redrunner]

Sounds like a "normal" situation to me. When mine sits for a few days without running I have to crank it a few times to get the fuel back to the carb. 4 or 5 seconds X 2 or 3 and we have lift-off.
I have a brand new mechanical fuel pump (spectra premium).

 

[nm9stheham]

Can just be evaporation of the fuel for the carb; try premium to see if that improves. If you are only used to modern fuel injected cars and the way the fire right off every time, this may just be an adjustment for you.

Alternately, the inlet and outlet check valves in the mechanical fuel pump are faulty or have a bit of crud in them. But more likely it is the first issue.

 

[MarPar]

pump it 6-7 times and crank it, pump another 5-6 times and crank it again...

 

[Garys1969RR]

Hi I have a Super Bee 1970 - 383 - with new tanked placed by previous owner. It had an electric fuel pump. I got the pump removed (was very noisy) and replaced by a mechanical one on the engine (and new inline filter). Initially OK. But when I leave the car for a few days the fuel has flowed back to the tank. It then takes a couple of cranks (5 or 6 generally) to get enough fuel and pressure back to start. Once started it runs fine.

where do I start looking or fixing (to avoid putting a new electric pump in)...? There are 2 outlets on the short side of the tank. One is sealed off - the other runs the single line to the front.

thanks
chr.

There should be enough fuel in the float bowls to start the engine after it's been sitting for a few days. Just pump it a few times to get the accelerator pump shooting fuel into the manifold. You need to have the fuel tank vented to the atmosphere. As fuel is drawn out, the tank will collapse if it is not vented. My 69 RR has 2 vent tubes on the tank, as well as the fuel line. One goes to the bottom of the tank on the inside, the other one goes to the top of the tank on the inside.

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The vent tubes rise way up into the trunk, to prevent fuel overflow when the tank is full. Then they curve sideways and back down into the area in front of the tank. You may be creating a vacumn condition in the tank which draws fuel back into it from the fuel pump.

 

[mopar 3 B]

If mine started like that after setting a couple day would toss the DP and install a carb that worked. To hard on the starter to crank it that long and see no need to flood it to start with. No choke on TQ use a primer bottle and starts right off.

 

[Mebsuta]

Mine does that with Edelbrock carbs. I have simple work-around, but I like it just the way it is because it's an old hot rod and being tricky to start kept it from being stolen one time.

 

[69hemibeep]

Mine does it also I think its the newer gas blends evaporate fast. I prime mine to save the starter and it seems it takes 2-3 days to evaporate. And that's both AFBs

 

[ArtH]

I had problems like that years ago and tried everything. Then I checked the rubber (or whatever flexible fuel line is made from) that connected the gas tank to the steel line that ran to the fuel pump. Eighteen inches (+/-) rotted junk that would not hold vacuum replaced it and all was well. I suspect when an older car sits for a few days, much of the gas in the carb bowl evaporates. The charcoal canister is designed to absorb those vapors and then suck them back into the carb once you start up. Old cars didn't have that and vented into the atmosphere. I usually have to crank the engine a couple times to get gas up into the carb and that problem seems to be common place is the car sits a few days.

 

[383man]

I use the Holley electric pump with an 850 DP. Mine can sit for weeks and all I do every time is pump the pedal 3 times to the floor and she fires right up every time. I use no choke as I removed it and if its real cold like below 32 degrees F then I give it one or two more pumps. Ron

 

[miller]

??? Does a non-vented tank, with a vented cap, and a phenolic (where's spellcheck, lol) spacer at the carb help any, when using AFBs or Edelbrocks?

 

[lewtot184]

Mine does it also I think its the newer gas blends evaporate fast. I prime mine to save the starter and it seems it takes 2-3 days to evaporate. And that's both AFBs

this! my r/t with the stock intake and avs will evaporate most of the fuel from the carb in 8hrs. the alcohol makes matters much worse. the quads on my 65 coronet will loose most of the fuel in the carbs in a couple of days.

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??? Does a non-vented tank, with a vented cap, and a phenolic (where's spellcheck, lol) spacer at the carb help any, when using AFBs or Edelbrocks?

all fuel tanks have some kind of vent so i don't think that a tube vent or gas cap vent makes a difference; you just need a vent. heat spacers do slow the evaporation down but are not a long term cure.

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i use one of those bottles with a discharge tube, like used to prime injectors, to fill the fuel bowls if my cars have set for several days. instant start up.

 

[coloradodave]

this! my r/t with the stock intake and avs will evaporate most of the fuel from the carb in 8hrs. the alcohol makes matters much worse. the quads on my 65 coronet will loose most of the fuel in the carbs in a couple of days.

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all fuel tanks have some kind of vent so i don't think that a tube vent or gas cap vent makes a difference; you just need a vent. heat spacers do slow the evaporation down but are not a long term cure.

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i use one of those bottles with a discharge tube, like used to prime injectors, to fill the fuel bowls if my cars have set for several days. instant start up.

X2 - It's the open system and current gas that evaporates super fast. I have 1" phenolic spacers on mine and they didn't make a difference. If I drive it everyday there is no problem. Even every other day, but if it sits 3-4 days, 10 seconds or so of cranking while stabbing the throttle several times to get it to light. Part of the 'charm' of a non fuel injected car...

 

[ArtH]

It's easy enough to test. Let the car sit a couple days and then lift the air cleaner. Pump the carb by hand a couple times while looking down the carb with a light. You should see a spurt of gas when you pump the carb. If not, the carb bowl is dry and as most people have pointed out, it's just due to evaporation. I hadn't thought of the alcohol being a factor, as I have always though gasoline is more volatile than alcohol. If you're in a hot dry area, Southwest for example, my thinking is it will evaporate much quicker. Colder, more humid just the opposite. You can do an experiment by putting a small amount of gas (how much does the fuel bowl in a carburetor hold) in a container with a small vent (about a 1/4 in diameter) and set it outside in an open area. Then see how long it takes evaporate.

I have been told lower octane gas tends vaporize quicker than higher octane and therefore contributes to detonation.

 

[wannadrag]

X2 went through this with a 68 GTX.The bowls generally fill from the top so it would be mighty hard to drain back and wasn't leaking to the engine.Its all the ethanol in the gas.

fuel isn't "flowing back"; it's evaporating.

 

[Garys1969RR]

Yes good point on the quick evaporation of todays fuels. I spilled some in the driveway, and time I had gone to get a rag to clean it up, it had all disappeared! He he.